Wikipedia:Reference desk/Archives/Science/2008 August 10

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 10

Herbivores and omnivores in same species

Are humans the only species in which some members are exclusively herbivorous and others aren't? NeonMerlin 00:20, 10 August 2008 (UTC)

Some cats are omnivorous. There might be other species whose diet is modified based on the availability of food. − Twas Now ( talk • contribs • e-mail ) 01:27, 10 August 2008 (UTC)

all humans are omnivorous, very few people have never eating plants or meats. even if many people choose to permanently eat both or either. i.e. most muslims know what pork tastes like, they've tried it, and many are made to try it so they can identify it.^MY♥_INchile 03:07, 10 August 2008 (UTC)

Careful, you don't want a fatwa. I strongly suspect that as most muslims live in countries or communities where Islam is endemic, pork simply isn't available, and the social penalty for eating it is severe. —Preceding unsigned comment added by 86.128.192.207 (talk) 17:40, 10 August 2008 (UTC)

Well, I know dogs are omnivores and can live on vegetarian diets or on mixed diets, as humans can. I imagine there are other species for which this is true too. I have a suspicion the same is true for pigs, but I can't find a reliable looking source either way right now. 79.66.38.215 (talk) 04:57, 10 August 2008 (UTC)

Clearly example is pyrhana, there are 2 types seperately (omnivore and herbivore)....Ninjaw —Preceding unsigned comment added by 124.120.200.29 (talk) 06:59, 10 August 2008 (UTC)

Note that being an omnivore isn't really a question of choice, it's a question of biology. Limiting yourself to a certain diet doesn't make you any less of an omnivore, even if it makes you a vegetarian. -- Captain Disdain (talk) 09:23, 10 August 2008 (UTC)

Also mosquitoes- the males are exclusively herbivorous and the females exclusively drink blood. Nadando (talk) 23:51, 12 August 2008 (UTC)

Wet wipe marker

i need help trakcing down sources for wet wipe markers, also known as chalk in or fluorescent markers, you know they ones they use on the outdoor menu displays at restaurants, that look like chalk but wont get all messy, yeah those. theres a bunch of alleged sources here, but i can't find them on their own, would anyone care to help?^MY♥_INchile 00:38, 10 August 2008 (UTC)

I'd try staples. --Shaggorama (talk) 14:37, 10 August 2008 (UTC)

I assume you mean Staples Inc., a US-based office supply store, not staple (fastener), a small metal clip used for holding paper together. I'll note that any major office supply store would be able to help the original questioner. -- 128.104.112.147 (talk) 19:37, 10 August 2008 (UTC)

Thank you for clarifying my comment. My phrasing was pretty confusing, and I'm sure no one would've understood what I meant besides the two of us. --Shaggorama (talk) 21:36, 12 August 2008 (UTC)

Density of human blood

Water is 1 gm/cc. what is blood density? please? —Preceding unsigned comment added by 79.76.242.64 (talk) 01:29, 10 August 2008 (UTC)

According to our Blood article its 1060 kg/m³. -hydnjo talk 01:49, 10 August 2008 (UTC)

Thats not much denser than water then!, So 8 pints of blood (the content on the human body) only weighs about 10 pounds? —Preceding unsigned comment added by 79.76.242.64 (talk) 02:00, 10 August 2008 (UTC)

If I typed the right numbers into Google calculator, it comes out to just under 9 pounds, but yes, it's barely more than water. --Tango (talk) 02:16, 10 August 2008 (UTC)

It would depend on whether you mean US or Imperial pints. Anyway, the number is about right. The Blood article says the typical volume in a human is about 5 liters, which would therefore weigh 5 × 1.06 = 5.3 kg or almost 12 pounds. But there'd be enough variation that you couldn't count on the second digit there. --Anonymous, 04:57 UTC, August 10, 2008.

True, I assumed US pints since usually online, if people don't specify, they're more likely to mean US. (I'm British, so it's not that I'm bias in favour of US measurements!) --Tango (talk) 05:13, 10 August 2008 (UTC)

If everything in the universe suddenly doubled in size, would it matter?

Would it be noticeable on some level? Like physical laws changing? I thought like Einstein and realized space is relative so at first I thought no. Then I remembered something- singularities. How could you double the "size" of that without seriously disrupting something? It would probably spawn some new emergent property with disastrous consequences! 0_0 -----Sam Science (talk) 01:38, 10 August 2008 (UTC)

Some formulas for natural phenomena include a parameter that is "squared". If everything doubled, these phenomena would be 4 times as great. That might produce unexpected results. Incidentally, I wonder why "squared" crops up so often in formulas for natural phenomena. An example is e=mc². There are many, many other examples. Why should something be multiplied by itself in natural phenomena? AndMe2 66.52.8.89 (talk) 02:19, 10 August 2008 (UTC)

A special case of this is that if you go from the first to the second dimension (length to area) you multiply lengths so you get squares. --Ayacop (talk) 06:45, 10 August 2008 (UTC)

The simplist way a squared can come up is because a factor appears in two different things that end up being multiplied. First thing that springs to mind is air resistance which is proportional to the square of velocity because velocity affects how many molecules of air you hit and how much energy you hit each one with. --Tango (talk) 02:29, 10 August 2008 (UTC)

With any "What would happen if this changed?" type question, it's important to state precisely what's changing and what's staying the same. How are you doubling the size of everything? You would need to change some physical constants appropriately (reduce the electric constant to increase the size of atoms, amongst other things). You have to make sure the physical laws are still obeyed, for example, ${c_{0}}^{2}\,\epsilon _{0}\,\mu _{0}=1$, (those are the speed of light, electric constant, vacuum permeability, in that order), so if you change the electric constant, you have to change either the speed of light, or the permeability to compensate. If you change everything just right, you wouldn't notice any difference (for example, if you doubled the speed of light, the speed of light measured in terms of the radius of one of the objects you've doubled the size of would be the same). --Tango (talk) 02:29, 10 August 2008 (UTC)

Let's consider what would happen if all objects doubled in linear dimensions without changing any physical constants or other material properties. The Earth is 8 times as massive, but its surface is twice as far from its centre, so the acceleration due to gravity at the surface is 2g. Your body is 8 times as massive as it was, so you weigh 16 times your normal weight. However, your muscles are only 4 times as powerful (muscle strength varies with cross-sectional area). You need 8 times as much oxygen as you do now, but your lungs' surface area has only increased by a factor of 4. Fortunately, the air is twice as dense (due to increased surface gravity) so you only need to breathe at the same rate as normal. But you are moving a chest that weighs 16 times its normal weight with muscles that are only 4 times as powerful. Doesn't sound like a pleasant experience ! Gandalf61 (talk) 10:05, 10 August 2008 (UTC)

It's an interesting interpretation, making macroscopic objects twice as big but keeping atoms the same (and just having more of them), but it's not that simple - if you make the Earth 8 times as massive the internal pressure will increase, increasing the average density and the radius won't be twice as big. To get the radius twice as big, you need more than 8 times the mass. There are also all kinds of other considerations. If the sun is also twice as big, and more than 8 times as massive (much more, I expect, the added pressure will be more significant than with the Earth), the Earth's orbit is going to change. You then need to decide what you want to keep the same - the size of the orbit (or, perhaps double that as well), the length of a year, the orbital velocity? Which you choose will change what to affects are. If you keep the orbital velocity the same, for example, you'll end up with a much closer orbit around a much more luminous star and the atmosphere would probably boil off - so much for the atmosphere being twice as dense! --Tango (talk) 20:43, 10 August 2008 (UTC)

William Poundstone covers this question in great and entertaining detail in Labyrinths of Reason. --Sean 14:37, 11 August 2008 (UTC)

Thremocouple power output

What is it? —Preceding unsigned comment added by 79.76.242.64 (talk) 02:34, 10 August 2008 (UTC)

Take a look at thermocouple and see if that answers your question. Otherwise, you'll need to be more precise about what you want to know. --Tango (talk) 02:58, 10 August 2008 (UTC)

Looked. Doesnt really help. I want to know the typical power output of a typical thermocouple or thermopile as used in flame failure devices. —Preceding unsigned comment added by 79.76.242.64 (talk) 21:12, 10 August 2008 (UTC)

A circuit's power is determined by its resistance and voltage; Ohm's law is a good approximation of the relationship for most materials. To find the power used by a flame failure device, you need to know bothy the electromagnet's resistance and the thermocouple's voltage. The latter is not enough.

I couldn't find any data for a typical electromagnet in a FFD, but hopefully another editor will be more successful. --Bowlhover (talk) 09:27, 11 August 2008 (UTC)

When our "gas log" fireplace needed some troubleshooting, I measured this. If memory serves, that particular thermopile was capable of putting out about 40 mA at some very low voltage. Half the current operated the "pilot light maintaining coil" in the gas valve and the other half operated the "main burner coil" in the gas valve. I took notes; if you really need to know the details, I can probably dig them up.

Atlant (talk) 19:30, 14 August 2008 (UTC)

Upthread, someone provided a link to a typical "large" Honeywell millivolt control valve. The specs for that valve state:

ELECTRICAL DATA: 
Pilotstat Power Unit - Hold-in 15 ma maximum; 
dropout 10.5 to 4.5 ma; resistance 11 ohms. 
Valve Operator - Pull-in 65 ma maximum; coil 
resistance 2 ohms. 

And state that the millivolt thermopile produces about 750 mV open circuit.

Atlant (talk) 21:06, 14 August 2008 (UTC)

Cooking Pasta

Standard instructions for cooking spagetti (and other dry pasta) are:

bring water to a boil, then put the pasta in the boiling water.

Is there any good reason to do it this way, or will it work just as well to put the pasta into cold or warm water, then bring the water to a boil?

Based on limited experiment, I suspect the latter is the case.

Thanks, Wanderer57 (talk) 02:54, 10 August 2008 (UTC)

It makes estimating the cooking time a little difficult, since it depends on how quickly the water heats up. Other than that, I can't see any problem. It's more energy efficient, however, to heat the water in a kettle and then add it to the pan already boiling - kettles heat the water quicker, so there's less time to lose heat. --Tango (talk) 03:01, 10 August 2008 (UTC)

Also, the pasta will tend to clump and stick together during the heat-up. -hydnjo talk 03:18, 10 August 2008 (UTC)

If you add a little olive oil, the pasta won't stick together. AndMe2 66.52.8.89 (talk) 03:25, 10 August 2008 (UTC)

I am not a science type but I am a chef. It makes little difference to the resulting pasta if we're talking about a single serving; a small portion in an amount of water that comes to a boil quickly. However, it makes a big difference if we're talking about a large amount of pasta in a corresponding large amount of water that takes a significantly longer time to come to a boil. What you want is al dente. I donlt know the exact scientific reason why but pasta which soaks for any length of time before coming to a boil doesn't yield al dente pasta. Instead, what you get is mushy pasta (mushy pasta=bad). There is another reason for putting the pasta in boiling water, and this applied to both large and small servings: you need to stir pasta to avoid clumping. putting the pasta in immediately means you're going to be standing over the pot stirring for a longer period of time. Efficiency in cooking matters a lot when you're doing it over and over. By the way, putting oil in pasta water as an inoculation against sticking isn't effective, is a waste of oil and shouldn't be done for a very good reason: the sauce wonlt stick well to the pasta, it slides off. Don;lt use oil in the water, just stir. Some other things you might want to know: always wash dry pasta in water just before you put it in the pot. This takes off the starch (if you put it in a bath you'll see how cloudy the water gets); you can't make good pasta without salting the water (use kosher salt, never iodized); Once your pasta is at the perfect state, and you've drained, add your sauce immediately which cools it down. If you take a bit mass of hot, al dente pasta and let it sit, it will continue to cook and voila, mushy pasta.--70.107.9.159 (talk) 03:47, 10 August 2008 (UTC)

Two thoughts about your practical observations:

1. Do you really come to a rolling boil first, or just gentle boil? A rolling boil could itself help avoid clumping by keeping the pasta moving around. That is, it's more than just reducing the need for "standing over the pot stirring for a longer period of time".

2. If soaking pasta leads to mush but plunging into boiling water gives good cooking, I wonder if the boiling water (nearly) instantly cooks the outside a bit (gelling the starch, or whatever happens when carbs "cook"), and this coating prevents the mushing. Either sealing out too much water or preventing the whole structure from dissolving (it's just a chunk of flour:). Something like searing a steak or blanching french fries?

Dang, now I'm hungry. DMacks (talk) 05:23, 10 August 2008 (UTC)

I second the "don't waist oil in the water" and add don't time it, throw your pasta at the window, wall, fridge or whatever "technique" used to time the cooking. Just TASTE it and soon you'll know exactly when they need, 30 seconds or a minute more to be exactly the way you like. 190.244.186.234 (talk) 05:54, 10 August 2008 (UTC)

Ants climbing trees

Recently while up a ladder to cut a branch off a tree, I noticed ants on the bark of the tree.

Why might ants go to all the work of climbing trees?

The tree was not doing something that might have provided food to the ants, like flowering or dripping sap.

Thanks, Wanderer57 (talk) 03:05, 10 August 2008 (UTC)

Cutting the leaves and collecting them for the nest is what I remember from a documentary. Don't they let themselves fall down with it, too? --Ayacop (talk) 06:36, 10 August 2008 (UTC)

Right at the tips of the branches there may have been herds of aphids being farmed by ants collecting the honeydew. Ants don't seem to know the meaning of distance and will walk a long way for some honeydew. Richard Avery (talk) 06:47, 10 August 2008 (UTC)

There appears to be only one kind of ant that does the cutting: leafcutter ant. --Ayacop (talk) 06:50, 10 August 2008 (UTC)

There are also ants that live in trees. See Acacia cornigera and Acacia drepanolobium--Lenticel ^(talk) 10:33, 10 August 2008 (UTC)

Thanks. I'm in southern Ontario, Canada, a long way from where leafcutter ants or those acacia species are found. I will take a closer look at the tree.

Maybe the ants just went up for the view. Wanderer57 (talk) 16:38, 10 August 2008 (UTC)

How do we know Planck measurements are the ultimate?

For example, how do they know the "smallest" planck length is 10 to the negative 20th power? Couldn't you just divide again? The problem could be scale. If something the size of the universe was trying to measure something on our scale it would be meaningless to observer.- And observed.--Sam Science (talk) 03:58, 10 August 2008 (UTC)

My not very well educated answer is that all quantum mechanics appears to work in multiples of the constant or the constant divided by 2(pi). There is not a single part of quantum mechanics that does not, so far as I can tell. Additionally, it has something to do with the c (the speed of light in a vacuum), and is thus clearly somehow integral to the very nature of the universe. In fact, with e=mc2, were Planck's constant infinitely small, c would be infinitely large, and there would be infinite energy in the universe. Unfortunately, Wikipedia's article on the constant is extremely lacking (Brittanica's article is much better).

Sorry for being so nonspecific. Magog the Ogre (talk) 04:24, 10 August 2008 (UTC)

You're getting confused between the Planck length and Planck constant, I think. --Tango (talk) 04:26, 10 August 2008 (UTC)

Yes but aren't they ultimately related? Magog the Ogre (talk) 04:29, 10 August 2008 (UTC)

In that the Planck constant is one of the constants used in the definition of the Planck length (together with the gravitational constant and the speed of light), yes. --Tango (talk) 04:31, 10 August 2008 (UTC)

Planck length#Physical significance has a thought experiment that tries to explain it. --Tango (talk) 04:31, 10 August 2008 (UTC)

Planck time is the amount of time that light takes to travel 1 Planck length; since a Planck length is the shortest measurable length and the speed of light is the fastest possible speed, 1 Planck time is logically the shortest meaningful amount of time. Planck temperature is the highest temperature at which matter remians matter, so it's the highest meaningful temperature.

It is not true that 1 unit in all Planck units represents the lowest or highest possible measurement. 1 Planck mass is much heavier than all fundamental particles, and 1 Planck charge is equal to the charge on 11-12 electrons. --Bowlhover (talk) 10:36, 11 August 2008 (UTC)

Centrifugal Sorting of Materials

OK. The rings of Saturn were not sorted by centrifugal force. I never quite believed it anyway.

But the discussion has led me to some further thoughts about centrifugal separation.

Assume a mixture of material is being separated in a centrifuge. Is the size of the particles significant in centrifugal separation? Conventional (high school) wisdom says "No". But I am wondering why.

To illustrate, let us say a quantity of glass marbles is mixed with a quantity of steel balls. The marbles and steel balls all have the same diameter. Each steel ball therefore has a greater mass than each glass marble. The mixture is put in a large centrifuge and spun. The steel balls will more strongly resist deviation from motion in a straight line and will push their way between the marbles. The steel balls will thus work their way to the outer edge of the spin path. The inevitable vibration (from imperfect bearings, etc.) would hasten the process. A thin coat of non-sticky lubricant on each ball would also assist by reducing friction as the balls slide past each other. Or for simplicity to establish the basic principle, we could assume there is no friction between any of the balls. (Centrifugal separation of gases avoids most of the friction, I think.)

Now imagine a mixture of glass marbles and lead shot. The marbles are all the same diameter. Each lead shot is the same diameter as other lead shot, but is small enough that it has less mass than each marble. Spin the mixture in a centrifuge. The marbles (having greater mass) will more strongly resist deviation from motion in a straight line Will the marbles work their way past the lead shot to the outer edge of the spin path? If so, the materials will become separated by their density, rather than their mass. Let us assume there is no friction.

I don't have an answer to this. Maybe someone can come up with one.

Andme2 (talk) 07:44, 10 August 2008 (UTC)

see Brazil nut effect. Saintrain (talk) 13:50, 10 August 2008 (UTC)

To clarify, if in the thought experiment you provide you are saying that the marbles and lead shot are the same diameter but different masses, then the brazil nut effect is inapplicable because it is a function of volume and not mass. --Shaggorama (talk) 14:34, 10 August 2008 (UTC)

I read OP that the lead shot were much smaller diameter; the weight of each shot is less than that of a marble. Saintrain (talk) 19:59, 10 August 2008 (UTC)

The effect occurs in spherical particles due to a function of volume, mass, and surface hardness. Volume is a major contributer, but experiments have shown that the other factors can overpower it easily. When the particles get non-spherical, we're in the realm of something physics has not yet been able to model. SamuelRiv (talk) 18:53, 10 August 2008 (UTC)

If we assume there is no friction, then I don't think surface hardness enters into it. I think the solution has to do with the fact that the center of each marble is more greatly spaced from the surface of the marble than is the case with the center of a lead shot. Andme2 (talk) 19:28, 10 August 2008 (UTC)

Brazil nut effect article says the effect is seen in mixtures "containing particles of different sizes but similar density". If particles have significantly different densities then the densest particles (note "densest" not most masive) will settle to the bottom/outside of the centrifuge because the centrifuge creates a pressure gradient. Gandalf61 (talk) 19:55, 10 August 2008 (UTC)

Let's try the Brazil nut effect with the marbles and lead shot. Put a mixture of them in a container and fasten the container on a shake table. Start the shaker.

There is no centrifugal force. But this shake table has a vertical component of motion. That frequently throws the marbles and lead shot upward, after which they fall downward.

This shake table also has a horizontal component of motion. As the marbles and lead shot fall downward, the shake table will exert a horizontal force that presses on the marbles and lead shot in contact with the sides of the container. These, in turn, press on some of the adjacent marbles and lead shot. Some of the lead shot will then be pushed a little way beneath some of the marbles. These marbles will rise in the mixture when all the material settles on the bottom of the container.

Some lead shot also gets pushed on top of some of the marbles during the fall. But these will tend to roll off the marbles when the entire mass comes to rest on the bottom of the container. In time, all the marbles will be on top.

By the way, the horizontal push exerted sequentially by each side of the container, together with the rising marbles, accounts for the convection current. In a cylindrical container, the horizontal push exerted sequentially to all sides of the mass is carried through the mass and meets more or less in the center of the container, where it all cancels out. (This convection current will be most noticeable when the particles are more similar in size and density.)

Now imagine the experiment is done with marbles and lead balls, with all spheres having the same diameter. The horizontal component will shove some lead balls part way beneath some marbles during the fall. But (statistically speaking) an equal number of marbles will be pushed under lead balls. There will therefore be no sorting due to horizontal motion.

To clarify the equal-diameter-spheres situation, imagine that only marbles of equal diameter are used. Some are green marbles and some are red marbles. Obviously there will be no sorting due to vertical motion followed by horizontal motion. There will be no wedging effect of small balls being pushed beneath large balls.

These thought experiments ignore the elasticity of the spheres, and permanent distortion of the lead balls that may be caused during the experiment. Air currents during the fall are also ignored. However, by weeding out extraneous elements, we can see the basic process. Extraneous elements can then be figured in later if needed.

Oh, one more thing. I said the force exerted by the shake table has a vertical component and a horizontal component. If these are exerted simultaneously in a curving manner, there will be a centrifugal force. This will be slight and has been treated as an extraneous element. But a special shake table could be built in which these forces are not exerted simultaneously.

Andme2 (talk) 22:57, 10 August 2008 (UTC)

Eucalyptas Tree,nor Cal

Greetings.

We have a stand of rather tall Eucalyptas tree in our yard.

We live in Carmel Valley,Ca

Just recently r deck in the back by the stand is getting bombed with PURPLE droppings,,looks like bird poooooooop, but it is a berry color..!!!

Not trying to stop it, just would like to know what the heck is really going on,,?

Regards.............and................Thanks --Ddemos (talk) 09:04, 10 August 2008 (UTC)

Is it mulberry season where you are? Julia Rossi (talk) 09:51, 10 August 2008 (UTC)

Bat shit is supposedly purple..87.102.45.156 (talk) 13:24, 10 August 2008 (UTC)

or the blackberry season? Richard Avery (talk) 14:51, 10 August 2008 (UTC)

Richard is onto it. Obviously, birds like to hang out in your grove of trees. It's the time of year when berries, cherries, wild grapes, and all that are all ripening, which birds love to eat. And, due to their need to constantly be as lightweight as possible, they poop it out nearly as quickly.

Ergo, don't make the mistake that an uncle of ours did: built an arbor to sit under in the summer, planted grapes to grow on the arbor (fast growing, big leaves, etc). Unusable once the grapes started to ripen!!

--Danh, 67.40.167.46 (talk) 23:04, 10 August 2008 (UTC)

Flu like symptoms

As I understand, flu like symptoms are a reaction of the body to a pathogen which arise in the process of immune defense. But how exactly are these symptoms (or what immediately causes them) helping to defend the pathogen? 93.132.159.115 (talk) 10:56, 10 August 2008 (UTC)

There are several symptoms which you are referring to, I presume. Coughing is the mechanism the body uses to clear the trachea of foreign matter, be it fluid or a solid. This is particularly relevent in Influenza and other upper respiratory tract infections like the common cold since the viruses bind on epithelial cells. The remaining symptoms, bar one or two, are more side effects of the infection rather than a method for helping to remove the virus. Fever, for example, is usually the result of pyrogens released by bacteria or viruses. However, such substances are also released by the cells of your immune system. This particular topic is covered in more detail here. Individual symptom pages usually have a mechanism section, so you may wish to try: Fatigue (medical), Sneeze, Fever and Headache. —Cyclonenim^T@lk? 12:16, 10 August 2008 (UTC)

Thank you for the links. The subsection fever#Usefulness of fever was something of the sort I was looking for. Sneezing and coughing are plain enough: coughing tells the nurse your still alive and she can't skip your lunch and sneezing helps distributing the microbes you already have to your room mates (I'm only half joking). The other articles are too general for my question. Also muscle ache is a symptom for which I'm not sure what it's good for. 93.132.159.115 (talk) 20:01, 10 August 2008 (UTC)

Nasal congestion is caused by the inflammation of nasal tissue, which in turn results from large numbers of white blood cells entering infected tissue. It's very beneficial in the nose because that is the main site of infection. --Bowlhover (talk) 10:23, 11 August 2008 (UTC)

The Matrix

What are the references to mdern physics in the movie The Matrix ? 69.157.227.243 (talk) 13:40, 10 August 2008 (UTC)

One of the points of the movie was that the main characters "hacked" the matrix and so could violate it's rules. Among those rules were the rules of physics. I don't think there was any reference to physics in general in the movie beyond the characters capacity to violate fundamental laws such as gravity. If you want to know what physical laws were violated, I'm sure other members of the RD will be happy to list a few for you. As far as "modern physics" goes, I typically take this phrase to mean materials studies, relativity, and quantum mechanics, which weren't referenced in the film (to the best of my knowledge). --Shaggorama (talk) 14:30, 10 August 2008 (UTC)

The Matrix, like most high-budget special-effects-filled Hollywood movies, is a travesty against physics. It's not even internally consistent, though I doubt the effects team had a physicist on board to ensure plausibility. Your only recourse is to suspend disbelief.

I can't recall any notable references to modern physics in the movie either, just plenty of special effects which confound good 'ol Newtonian mechanics. -- 98.26.182.245 (talk) 17:53, 10 August 2008 (UTC)

And, if memory serves, the purpose was to harvest energy from humans. We're pretty inefficient energy sources. Much better to kill us all and burn the corn. Saintrain (talk) 20:02, 10 August 2008 (UTC)

Sorry this is off topic but I can't help: kill us all and burn the corn is one way, burn the corn so we'll die is another (I put your tortilla in my tank) 93.132.159.115 (talk) 20:22, 10 August 2008 (UTC)

There's a web site that reviews movies on how believable their physics are. Wisely, it chooses not to nit-pick the scenes inside the Matrix (since technically as a computer simulation there's no need for it to follow the laws of nature), but it's got a lot to say about the out-of-Matrix scenes. Confusing Manifestation(Say hi!) 23:04, 10 August 2008 (UTC)

They got it backwards. It's implied that the world we live in now is the matrix, and thus what we believe is the laws of nature is really the matrix' physics engine. This would mean that the physics in the matrix would be the same as in the real real world. The movie real world, on the other hand, could vary well have humans as perpetual motion machines, and the people in the matrix would have no way of knowing. — DanielLC 00:16, 11 August 2008 (UTC)

The Matrix is said to be an accurate simulation of late 20th century Earth, so the laws of physics should be the same in the matrix and out of it. The difference is that in the matrix, you can break those laws. --Tango (talk) 01:01, 11 August 2008 (UTC)

Animals

Do animals get zits? If they do can they squeeze them? —Preceding unsigned comment added by 86.128.192.207 (talk) 17:15, 10 August 2008 (UTC)

Yes they do get pimples all right. The fur tends to hide them from view. They could probably make an attempt at squeezing them, but why bother? Squeezing is usually for aesthetic purposes and as noted one can't see the spots. Fribbler (talk) 17:58, 10 August 2008 (UTC)

Umbilical Cord

Do animals have umbilical cords? If so, what do wild animals do with them? Humans usually cut them and tie them up, but of course animals can't do the tying, so what happens? I am just thinking this, because they must have them, otherwise the foetus would not be able to feed inside the mother. I've seen calves getting born, and they just seem to 'fall out', so to speak, totally unattached. Does it just come off inside the mother? If so, why is a human umbilical so long?--ChokinBako (talk) 17:44, 10 August 2008 (UTC)

Yes, mammals are all born with umbilical cords. Mammals are born with an umbilical cord attached to the placenta, which is also expelled from the mother. If left uncut the umbilical cord will "drop off" in a matter of days. Fribbler (talk) 17:54, 10 August 2008 (UTC)

Well, all placental mammals. Not sure what if any analogous structure is present in eggs. DMacks (talk) 18:08, 10 August 2008 (UTC)

See Placenta#Non-humans. There's not a lot of information there, but it answers your question. --Tango (talk) 18:12, 10 August 2008 (UTC)

I can say for certain that i've seen a cow giving birth to a calf and it promptly ate the umbilical cord and spent the next 10/20 minutes cleaning the little calf up. Was very interesting to watch as it gave birth (unaided) in the corner of a field, it was also amazing how quickly the calf could walk - it was only a matter of minutes before it was stable enough to move around without looking like bambi on ice. No idea if eating the cord is common in other animals but I recall hearing that it helped produce extra-rich milk for the baby (though I wonder if that's just an old wives tale).ny156uk (talk) 22:15, 10 August 2008 (UTC)

I can say for certain that I have seen well over a hundred cows giving birth. In my experience, they don't chew on the umbilical cord still connected to the calf (which is a short piece and dries up as Fribbler says). They do eat every scrap of the afterbirth. I believe this accomplishes two functions - remove the smell from the attention of predators and recover the nutrient-rich material. I don't believe that this helps to make the milk extra-rich though, colostrum is always expressed in the first 24 hours of lactation and is available immediately. The nutrients in the placenta probably help the cow recover from her ordeal though, and tide her over for the first while when she only pays attention to her calf and doesn't eat any grass. And yes, the first thing a cow does is lick every inch of her calf. This does two things - free mucus from the calf's hair so that it can start taking it's natural insulating effect; and the rough surface of the cow's tongue has a stimulative effect on the calf, helping to get its circulation going. The continued licking stimulates the calf to start stretching its muscles. Even if the calf is born not breathing, the mother's tongue can stimulate the calf to get started. We of course would jump in, clear the calf's throat of the mucus plug (breathing or not) and rub it with straw. In the not-breathing situation, we were much more rough, hanging it upside-down and pounding on it. Never lost one that way though. (/off-topic rant, anyone wanna see my photos? :) Franamax (talk) 00:36, 12 August 2008 (UTC)

I've also heard that it hides the evidence to keep from attracting predators. DMacks (talk) 04:27, 11 August 2008 (UTC)

It is long so that baby can make some movements inside and does not break abruptly when baby is delivered.

I too remember having seen on Discovery an animal eating placenta. Umbilical_cord#The_umbilical_cord_in_other_mammals is often consumed by the mother.

Interestingly, some fish (shark) do not have placenta. See Shark births. manya (talk) 04:46, 11 August 2008 (UTC)

I don't think any fish have placentas. Only placental mammals do. What's interesting is that some sharks' eggs hatch while still inside the mother, normally eggs leave the mother before hatching. --Tango (talk) 16:52, 11 August 2008 (UTC)

That caught me off gaurd too, but Google does tend to indicate that some sharks develop a placenta. [1] Presumably it is a result of convergent evolution, since sharks and mammals are on very different parts of the tree of life and so must have acquired the ability independently. Dragons flight (talk) 18:49, 11 August 2008 (UTC)

Placentophagy is the practice of eating the placenta. A number of non-mammals are viviparous, and some of these do have placentæ. DuncanHill (talk) 18:15, 12 August 2008 (UTC)

Bismuth tin alloy

I bought some bismuth tin alloy in the form of shot for some magnet experiments. i was expecting it to be strongly diamagnetic, but I dont get any effect with NIB magnets brought close to it. Is Bismuth tin (the alloy) diamagnetic, of does it have to be pure bismuth? —Preceding unsigned comment added by 79.76.242.64 (talk) 20:34, 10 August 2008 (UTC)

I will just mind my own bismuth on this question. Edison (talk) 00:38, 11 August 2008 (UTC)

Maybe thats wise, as you seem to have developed quite a nasty lithp there! —Preceding unsigned comment added by 79.76.242.64 (talk) 02:08, 11 August 2008 (UTC)

The intro of the alloy article tells us that an alloy "usually has different properties from those of its component elements." Even if the alloy were the sum of its parts, you have to consider that adding tin "dilutes" the amount of bismuth present (therefore reducing its effect). At an extreme, maybe even the tin could counteract the bismuth (an extreme case would be perfect cancellation, for example US 5294268 ).

But in fact, the exact magnetic properties of Bi–Sn alloy have been studied (J. F. Spencer; M. E. John (Sep. 1, 1927). "The Magnetic Susceptibility of Some Binary Alloys" (login/subscription required). Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character. 116 (773): 61–72. {{cite journal}}: Check date values in: |date= (help)) and the relationship of the ratio of the two metals in alloy to the magnetic susceptibility of the alloy is not simple at all. Not all ratios of the two metals given a magnetic alloy (and even the sign of the magnetic susceptibility changes!). DMacks (talk) 05:01, 11 August 2008 (UTC)

Apologies for not doing more research. The author of this webpage, just like you, tried levitation using the bismuth-tin alloy and failed because the shot was 3% tin. Interestingly though, these people were successful, although the shot they used might have been pure bismuth. --Bowlhover (talk) 22:52, 12 August 2008 (UTC)

Yeah Id seen the second link: thats where I got the idea. But not the first link-- thanks. I thought all bismuth shot would be approx the same composition (ie 1% to 3% tin). How do you know what you are using when shooting those little birdies? —Preceding unsigned comment added by 79.76.184.142 (talk) 00:00, 13 August 2008 (UTC)